The present invention relates to a microwave oven and, more particularly, to a microwave generation suppression system in a microwave oven when a microwave oven cavity temperature rises to an abnormal value.
There is the possibility that an oven cavity temperature can rise to an abnormal value due to the combustion of foodstuff or under a no load operation. It is important that the microwave generation be suppressed when the oven cavity temperature rises to an abnormal value.
In the conventional microwave oven, a heat-sensitive fuse is disposed in a power supply circuit for the microwave generation control circuit for suppressing the microwave generation when the oven cavity reaches an abnormally high temperature. In the prior art system the heat-sensitive fuse is disposed on the oven wall, on a wall of an exhaustion duct, or in the oven cavity.
For example, U.S. Pat. No. 3,527,915 entitled "NO LOAD SENSING DEVICE FOR MICROWAVE OVENS", disclosed a microwave oven, on Sept. 8, 1970, wherein the no load sensing theremostat is placed within the cavity of the microwave oven.
The electrical isolation between the heat-sensitive fuse and the microwave oven wall or a duct wall must be strictly performed to ensure stable operation of the microwave oven and the heat-sensitive fuse. The heat-sensitive fuse must be tolerant of high temperature moisture, since the heat-sensitive fuse of the prior art is always exposed to the high temperature moisture. Moreover, it is very difficult in the prior art system to determine the set temperature of the heat-sensitive fuse, because the heat-sensitive fuse is always exposed to the high temperature moisture even when the microwave oven is in the normal condition.
Accordingly, an object of the present invention is to provide a microwave oven wherein microwave generation is suppressed when an oven cavity reaches an abnormally high temperature.
Another object of the present invention is to provide a novel temperature detection system for suppressing microwave generation when an oven cavity reaches an abnormally high temperature.
Still another object of the present invention is to stabilize the operation of a heat-sensitive fuse for detecting the abnormally high temperature of an oven cavity.
Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
To achieve the above objects, pursuant to an embodiment of the present invention, a hot air exhaustion opening is formed in an oven wall of a microwave oven in addition to a normal exhaustion opening. A heat-sensitive filter film made of, for example, a polyester film is disposed at the hot air exhaustion opening so as to close the hot air exhaustion opening when the microwave oven is placed in the normal operating mode. When the oven cavity reaches an abnormally high temperature, the heat-sensitive film is fused, thereby conducting hot air toward the outside of the microwave oven cavity through the hot air exhaustion opening.
A heat-sensitive fuse is disposed on the downstream side of the heat-sensitive film so that the heat-sensitive fuse receives and senses the hot air exhausted through the hot air exhaust opening when the heat-sensitive film is fused, that is, only when the oven cavity reaches an abnormally high temperature. The heat-sensitive fuse is associated with a microwave generation control circuit in such a manner that the microwave generation is suppressed when the heat-sensitive fuse is fused.
In a preferred form, the heat-sensitive film becomes fused at about 260.degree. C., and the heat-sensitive fuse is broken at about 115.degree. C. Therefore, when the heat-sensitive film is fused, the heat-sensitive fuse functions to suppress the microwave generation.